Machine Selection for Hot Isostatic Pressing

aPriori selects the lowest-overhead machine whose hot zone dimensions can accommodate the part dimensions.

A machine's hot zone dimensions can accommodate the part dimensions if both the following hold:

• Machine property Hot Zone Height is no less than the part's longest dimension.

• Machine property Hot Zone Diameter is no less than the diagonal of the projection of the part bounding box along the longest dimension (that is, the diagonal of a face of the bounding box that is orthogonal to the longest side of the bounding box).

Overhead, here, is the given by the following:

((Number of Batches *

(Direct Overhead Rate + Indirect Overhead Rate)) / Production Volume)

where

• Number of batches is the number of batches needed to achieve the production volume, given a batch size consisting of the maximum number of parts that can be accommodated by the machine (see below).

• Direct overhead rate is specified by a machine property.

• Indirect overhead rate is specified by a machine property.

• Production volume is specified in the Production Scenario tab of the Cost Guide.

The number of batches required for the current production volume is the result of rounding up the quotient of the production volume and the maximum number of parts that can be accommodated by the machine in one cycle:

Number of Batches = roundup(Production Volume / Max Number of Parts)

The maximum number of parts is determined as described in Number of Parts for Hot Isostatic Pressing.

Number of Parts for Hot Isostatic Pressing

The maximum number of parts that can be accommodated by the machine in a cycle is determined in one of two ways:

• Part-projected-area method: based on the dimensions of the part's bounding box (the GCD properties Length, Width, and Height)

• Part-volume method: based on the volume of the part (the GCD property Volume)

Part-projected-area method: By default in starting point VPEs, the maximum number of parts that can be accommodated by the machine is determined based on the following assumptions:

• Parts are oriented in the hot zone with the longest dimension running up and down.

• If the part's longest dimension is small enough relative to hot-zone height, there are multiple layers of parts.

• Parts have associated nesting allowances:

o Minimum horizontal distance between parts is specified by the cost model variable hipHorizontalNestingAllowance (13mm in starting point VPEs).

o Minimum vertical distance between parts is specified by the cost model variable hipVerticalNestingAllowance (10mm in starting point VPEs).

• Number of layers is the result of rounding down the quotient of the following:

o Hot zone height

o Part's longest dimension plus vertical nesting allowance

• Number of parts in each layer is the quotient of the following:

o Area of the hot-zone floor, that is (Hot Zone Diameter/2)2π

o Area of the projection of the part's bounding box (augmented by horizontal nesting allowances) along its longest dimension (that is, the product of the shortest two part dimensions augmented by horizontal nesting allowances)

With this method, the maximum number of parts is the result of rounding down the product of the number of layers and the number of parts per layer:

Max Number of Parts =

rounddown(Number of Layers * Number of Parts per Layer)

This result is subject to the constraint that the volume of this number of parts does not exceed the available hot zone volume (see below). If this constraint is not satisfied, the Part-volume method is used.

Part-volume method: Alternatively, the maximum number of parts is the result of rounding down the quotient of the following quantities:

• Volume of the hot zone that can be occupied by parts (the remainder must be occupied by the process gas)

• Part volume

Max Number of Parts =

rounddown(Max Fraction Occupied by Parts * Hot Zone Volume / Part Volume)

The maximum fraction of the hot zone that can be occupied by parts is specified by the cost model variable hipMaxPercentageSolidVolumeFromHotZoneVolume (0.6 in starting point VPEs).

By default in starting point VPEs, the part-projected-area method is used. Administrators can customize the default with the cost model variable defaultPartLoadingMethod (set to Part Projected Area or Part Volume). Users can override the default on a part-by-part basis with the setup option Part Loading Method.